Railway traffic controlling apparatus



Feb. 1934- e. w. BAUGHMAN |-:-r AL 1,948,197

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Oct. 17, 1932 2 ov- L 25 2 f G war/wad Mm 4 a M1 fli 4 Subsmion f g 5 5 r I: p 1- E3 I g I? .Z

W 1.1 9 IZ\ 1/ Z 1 I1 I INVENTORS l 11 a George WBaug/mmn Subslfaion M J I 6 Fran U1 M'cizolsan 10 BY QRW g) I will? ATTORNEY.

Patented Feb. 26, 1934 UNITED STATES PATENT OFFICE RAILWAY TRAFFIC CONTROLLING APPARATUS George W. Baughman, Pittsburgh, and Frank H.

Nicholson, Edgewood, Pa.,

assignors to The Application October 17, 1932. Serial No. 638,050

4 Claims.

Our invention relates to railway traific controlling apparatus, and more specifically to apparatus for the elimination of interference with the proper and safe operation of the locomotiv carried and wayside signaling equipment, caused by harmonics of the propulsion current of an alternating current propulsion railroad.

We will describe one form of apparatus embodying our invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a schematic diagram of an electrified railroad arranged for both alternating and direct current propulsion, showing one condition under which harmonics of the alternating propulsion current may exist in practice, and may cause undesirable and dangerous interference with the train governing equipment. Fig. 2 is a diagrammatic View showing the method and apparatus embodying s our invention for overcoming the interference caused by propulsion current harmonics.

It has been found expedient by some railroads, particularly in territory adjoining large railroad terminals, to operate both alternating and direct current locomotives over the same tracks, or over parallel electrically cross-bonded tracks. As is well known, where alternating current track circuits are used in alternating current propulsion territory, the signaling frequency employed is F a usually substantially different and most generally higher than the propulsion frequency in order that sharp selection can be made by frequency selective track relays or by locomotive train control receiver equipment tuned to the particular frequency, to remove the danger of false signals being produced by the propulsion current. If the propulsion frequency is cycles, for example, the signaling frequency commonly employed is or 100 cycles per second, usually the latter, in order to avoid foreign current interference with sensitive train control equipment from 60 cycle commercial power sources.

Usually, no objectionable interference with signaling circuits results from the presence of propulsion current of a given frequency interacting with the higher frequency signaling current. because the propulsion current is nearly always comparatively free from harmonics, and if harmonics are present, these are usually of the odd series such as the third, fifth. seventh, etc., the frequency of any one of these being sufficiently far removed from the signaling frequency to create no difficulty. It may properly be assumed however that with a signaling frew quency of 100 cycles, it is possible under certain conditions for the 25 cycle propulsion current to contain even harmonics, such as the fourth, for example. It will be apparent, that if this fourth, or 109 cycle, harmonic current is of sufficient magnitude and is unequally distributed between the two rails of the track with respect to the locomotive receiver or pick-up equipment, it may readily cause false or undesired response of the signaling apparatus. Where such a possibility exists, it becomes of the utmost importance from the standpoint of safety of train operation to eliminate this potential source of danger.

Harmonics of the even series, such as the above, have been observed under certain conditions met with in practice, and the manner in which these 0 even harmonics are produced will now be explained in order that the application of the corrective apparatus embodying our invention will be more clearly understood.

Referring to Fig. l, the reference characters 1 and 2 represent the two rails of a track section D-E, which provide a path for the track circuit signaling current and which serve, at the same time, as the common return for the alternating current propulsion system as well as for the direct current propulsion system. The reference characters G and G designate the direct current and alternating current propulsion generators, respectively, a direct current locomotive driven by the motor M and an alternating current locomotive driven by the motor M being represented diagrammatically by the wheel pairs L and L respectively. The impedance bonds IB at each end of the track section D-E provide a propulsion current path around the insulated rail joints, in the usual manner.

When the alternating current locomotiveL is operating, the current supplied to motor M through transformer T flows over a path which may be traced from one terminal of Winding 3 5 of transformer T overhead wire 4, pantograph P, winding 5 of transformer T, wire 6, rails 1 and 2 in parallel, bond IB at location D, and wires 7 and 8, to the other terminal of winding 3. If the direct current locomotive L is operating, the

current path for motor M extends from one tertrack relays as well as the locomotive train control equipment. The signaling current follows a series path through rails 1 and 2, whereas, the alternating current and direct current propulsion currents follow a path through these two rails in parallel.

Let it be assumed in Fig. 1 that the alternating current locomotive L occupies section DE, as shown, and that the direct current locomotive L is operating on the same track or on a parallel cross-bonded track. Under this condition, there will exist two multiple return paths for the direct current propulsion current, the first including rails 1 and 2, and the second including wire 6, winding 5 of transformer T, overhead wire 4, winding 3 of transformer T and wire 8. If, for any reason, an appreciable amount of the direct current propulsion current flows over the second path, a saturation effect will be produced in the primary winding 5 of transformer T, with consequent marked distortion of the wave of magnetizing current taken by this transformer.

It has been found that in addition to the commonly observed odd harmonics, numerous even harmonics of the 25 cycle propulsion current such as the second, fourth, sixth, etc., having frequencies of 50, 100, and 150 cycles per second, respectively, are present in appreciable quantities when direct current saturation exists in transformer T. Since the magnetizing current path for transformer T includes the rails 1 and 2, the dangerous interference from harmonics of the order of the signaling frequency will be clearly apparent.

If the magnetizing current for transformer T divides equally between the rails 1 and 2, there will usually be no effect upon the track relays, which are dependent upon a series rail path for energization; neither will this current affect the locomotive receiver equipment which is designed to respond to current of signaling frequency flowing in the two rails in series, and not to balanced rail currents flowing in the two rails in multiple. However, if the above magnetizing current containing even harmonics such as the fourth is, for any reason, unequally divided between rails 1 and 2, it will act as so much steady 100 cycle signaling current, and may falsely energize the track relays if these are of the single element type, and may interfere with the proper operation of the cab signals by filling in the off code periods in, the chain of train control code impulses which are used as one means for providing distinctive cab signal indications aboard the 10- comotive. Such unequal distribution of the current drawn by winding 5 of transformer T may result in the case of double rail track circuits from a broken rail, broken rail bond connection, or any other cause tending to create unequal impedances in the two rail paths. The interference will, of course, be accentuated in track circuits of the single rail type.

In addition to the types of interference mentioned above, there exist other possibilities of dangerous interference with the locomotive-carried train control equipment which will be understood more clearly in connection with a description of the diagram of Fig. 2.

Referring to Fig. 2, the reference character A designates the train-carried portion of the cab signaling equipment aboard the locomotive L which is shown occupying track section E-F. When the control winding 13 of the two element track relay TR becomes deenergized due to the entrance of a train into section EF, relay TR will release, opening front contact 14 to release the normally energized code-starting relay V. As soon as relay-V releases, the code transmitter CT becomes energized over back contact 16 of relay V, and at the same time, steady energy is removed from local winding 15 of relay TR by front contact 17-l8 of relay V, and a circuit is prepared by the closing of back contact 17-19 of this relay for the application of coded current to winding 15 of relay TR, for picking up the track relay as soon as the train leaves section E-F.

When the code transmitter CT becomes energized, the mechanism of the code transmitter will cause contacts 180 and to open and close at the rate of 180 and 80 times per minute, respectively. If the track section DE is unoccupied, front contact 20-21 of track relay TR will be closed, and current of 180 code will be supplied to track transformer T and local winding 15 of relay TR, over a circuit which includes wires 23 and 2 1, front contact 186 of coder CT, wire 25, front contact 2il21 of relay TR wire 26, back contact l7-19 of relay V, and wire 2'7, to transformer T and winding 15. If, however, the section D-E is occupied, back contact 2022 of relay TR will be closed, and current of 80 code will be supplied to the rails l and 2 and to winding 15 over contact 80 of coder CT and back contact 2022 of relay TR Assuming that 180 or proceed code is being supplied to rails 1 and 2 by transformer T the rail flux established by this current will induce cumulative voltages in the two windings 28 and 29 of the locomotive receiver, the resultant voltage being applied across the input terminals of the filter unit F. Since the filter F is designed 110 to pass freely currents of 100 cycle frequency, this voltage will be applied to the grid of tube VT and will produce an amplified first stage plate current which, through the interstage transformer T, will cause an amplified voltage to be applied to the negatively biased grid of the second stage tube VT resulting in unidirectional pulses of 100 cycle current, corresponding to the on code periods, in the plate circuit of tube VT The second filter circuit comprising winding 30 of master relay transformer T and condenser C is designed to smooth out the 100 cycle pulses, passing freely low frequency pulses of the order of 2 or 3 cycles per second. Therefore as each 125 pulse of current representing an on code period is initiated, flux will build up in transformer T only to die down aga n during the off code period. These periodic increases and decreases in the flux of transformer T will induce periodi- 130 cally reversed voltages in winding 31, causing contact 32 of the polarized master relay MR to operatein step with the 180 per minute code impulses supplied to rails 1 and 2.

The periodic reversal of contact 32 of relay 135 MR causes direct current to flow alternately in one and then the other half of winding 33 of transformer T so that an alternating current voltage of the code period frequency will be induced in winding 34 for operating the selectively 14,0 responsive relays R or R according as the code frequency is 180 or 80 periods per minute, re spectively. The relays R and R in turn, control cab signals S and S Having thus far described the normal operation of the cab signaling equipment, we shall now explain the manner in which harmonics of the propulsion current may, under certain conditions, produce improper operation of cab signals s and S Let it be assumed that the 25 150 cycle propulsion current flowing in rails 1 and 2 is unequally divided between these rails and contains a fourth or 100 cycle harmonic of appreciable magnitude. The unbalanced fourth harmonic rail current will create a net resultant voltage in receiver windings 28 and 29 which will be passed through filter F and tubes VT and VT to transformer T. This voltage, being of steady character, will not of itself cause operation of the master relay MR, but it will be apparent that it may fill in the off code periods of the 100 cycle signaling current and may distort the on code second stage plate current, thereby interfering with the proper operation of relay MR and with the indication of the cab signals S and S Suppose now that locomotive L is operating over a track circuit the rails of which are carrying uncoded or steady signaling current, which condition is frequently made use of in practice, or that the code transmitter CT of Fig. 2 fails to operate, for any reason, such as a broken wire, etc. Since the steady signaling or code carrier current frequency bears no fixed relation to the propulsion frequency, the signaling current being usually supplied from an induction motor or gas engine driven alternator, the signaling frequency may vary from a nominal value of 100 cycles to a value several cycles removed therefrom, depending upon the load on the system, motor voltage, etc. Assume that this carrier frequency is 97 cycles. Both the 9'? cycle signaling current as well as the fourth harmonic 100 cycle current will be passed by filter F, so that both currents will be found in the plate circuit of tube VT The interaction of the 97 and 100 cycle currents will result in a modulation effect, giving rise to a 3 cycle per second or 180 cycle per minute beat note, which is of the exact frequency corresponding to 180 or proceed code in the rails. The master relay will therefore respond to the beat note and a false proceed in dication may result. If the signaling frequency is 98 cycles, a 1 cycle beat note may result which corresponds to a code frequency of 80 per minute, thereby producing an undesired approach.indication of cab signal S Apart from the single modulation effect described above, beat notes of a frequency to which the master relay will respond can also be produced by a double or compound modulation effect. For example, assume that the unbalanced propulsion current contains not only a fourth harmonic, but also a prominent third harmonic, and that the signaling frequency is 90 cycles. The modulation of the 90 cycle wave by the fourth harmonic will produce a 10 cycle beat note, and by the third harmonic, a cycle beat note, the interaction of the 10 and 15 cycle waves produc ing a 5 cycle beat note to which the master relay may be sufficiently quick acting to respond. Practical investigation of this problem has disclosed numerous combinations of propulsion current harmonics with the inconstant' frequency signaling current, which may produce undesired and dangerous interference with the proper operation of signaling equipment.

In order to eliminate the above hazard to railway traffic, we have provided means for maintaining the signaling frequency in fixed relation with the frequency of the propulsion current and therefore with the frequency of its harmonics, and have also determined upon a signaling frequency which is intermediate with respect to a pair of consecutive odd and even harmonics of particularly dangerous magnitude and frequency, this frequency being so chosen that beat notes arising from either single or double modulation will be of too high a frequency or of insufiicient magnitude for the master relay to follow. We have accomplished this result by providing a synchronous motor SM supplied with power from the propulsion mains and mechanically coupled to an alternator G which, in turn, energizes the high voltage signal transmission line 36.

We have found that the harmonics most likely to produce interference with the 100 cycle signaling current are the third, fourth and fifth, having frequencies of '75, 100 and 125 cycles, respectively, the frequency of the second harmonic, as well as of those greater than the fifth being too far removed from the signaling frequency to produce dangerous combinations. From the standpoint of master relay operation, a synchronously generated signaling frequency of 87 cycles, midway between the third and fourth harmonics, or a signaling frequency of 112 cycles, midway between the fourth and fifth harmonics, would be equally well suited to eliminate interference.

Taking 87 /2 cycles as an illustration, the frequency resulting from single modulation by the third or fourth harmonics would, in either case, be 12 /2 cycles, which is too rapid for the master relay to follow because the usual type of this relay when energized from the resonant circuit including transformer T and condenser C is incapable of following a frequency greater than approximately 6 cycles per second. Also, the double modulation effect of the third and fourth harmonics would disappear because there can be no frequency modulation of one 12 cycle wave upon another 12 cycle wave. Likewise, the single or double modulation effects produced by the fifth and sixth harmonics, or combinations of these with the third and fourth, would, in each case, result in frequencies too rapid to affect the master relay. Similar considerations would hold for a signaling frequency of 112 cycles.

However, since the presence of both alternating current and direct current propulsion currents is confined to limited sections of railroad territory, and the same train control'equipped locomotives must also operate over territory having alternating current propulsion only on which it is advantageous to use a signaling frequency of 100 cycles which has given highly satisfactory results, there presents itself the problem of providing receiving equipment on a locomotive which will be responsive to both 100 cycle signaling currents and also to signaling currents of a frequency determined by the harmonic interference problem.

One method of solving this problem is to design filter F in such manner that it will pass the frequency band established by the above two signaling frequencies as limits. For maximum efficiency of the band-pass filter under the given conditions, it is desirable to make the frequency band as narrow as possible. That is, although 87 /2 cycles is the ideal frequency with respect to the third and fourth harmonics, yet, the appreciable time constant of the master relay permits the use of a slightly higher frequency, thus narrowing the frequency band. For example, a frequency of 91 cycles per second provides single modulation frequencies with the third and fourth harmonics of 16 /3 and 8 cycles, respectively, the double modulation of these two resultant frequencies producing a frequency of 8% cycles.

Since the master relay will not respond to frequencies greater than 6 cycles per second, it will be apparent that 91% cycles is a safe frequency under the above conditions, and permits the use of a more efficient band-pass filter. By a similar procedure, the interference from any pair or group of particularly dangerous harmonics can be eliminated.

Although we have used 100 cycle signaling and 25 cycle propulsion frequencies as illustrative of conditions met with in practice, it will be apparent that numerous other frequency combinations can give rise to harmonic interference troubles which can be readily overcome by determining upon a particular frequency in the manner de scribed herein, and maintaining a fixed relation of this frequency with the propulsion frequency by means of synchronous generation either from the propulsion mains, or by a mechanical connection with the power unit which drives the propulsion generator.

Although we have herein shown and described only one form of railway traffic controlling apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. A train control system of the coded alternating current track circuit type for alternating current propulsion railroads in which the propulsion current fiows through at least one rail of the track, said propulsion current containing harmonies of its fundamental frequency, characterized by synchronous generation of the track circuit current with respect to the propulsion current at a frequency determined in such manner that the beat frequency of said track circuit current with each of two consecutive harmonics of said propulsion current as well as the beat frequency resulting from the interaction of said two beat frequencies is greater than a predetermined value.

2. In combination. a train control system having a coded alternating current track circuit at least one rail of which carries alternating propulsion current which is distorted by harmonics, a source of said propulsion current, a synchronous motor energized from said source, an alternator having a positive driving connection with said synchronous motor, and means for supplying said track circuit with current from said alternator in order that a constant frequency relation will be maintained between said two currents to minimize interference from harmonics of said propulsion current with said track circuit current.

3. In combination, a. train control system having an alternating current track circuit at least one rail of which carries alternating propulsion current distorted by harmonics, said track circuit being supplied with current of a given frequency generated synchronously with respect to said propulsion current for maintaining a constant fre quency relation therewith to minimize interference from said harmonics with said track circuit current, a rail vehicle, a receiver on said vehicle arranged in inductive relation with the rails of the track and having a band-pass filter designed to pass induced currents of a predetermined frequency band which includes said given frequency, and train governing apparatus controlled by said receiver.

4. In combination, a section of railway track at least one rail of which carries alternating propulsion current, means for supplying coded alternating signaling current to the rails of said section, said coded current comprising periodically recurrent on and off intervals, a control relay, a tuned receiving circuit for energizing said control relay from the signaling current flowing in the rails of said track, and means for maintaining a synchronous relation between said signaling current and said propulsion current, the frequency of said signaling current being determined with reference to the frequency of said propulsion current in such manner as to prevent filling in of the off intervals in said code by harmonics of the propulsion current as well as to prevent response of said control relay to beat notes result ing from the interaction of said harmonics with said signaling current.

GEORGE W. BAUGHMAN. FRANK H. NICHOLSON. 

